The creation of a dental prosthesis requires very precise fit and alignment to the prepared tooth, as well as to the adjacent and opposing teeth. In this discussion, a prosthesis may be a crown for a single tooth or a bridge to replace a number of teeth. In general, the dentist is concerned with achieving the proper fit for: the prosthesis and the prepared tooth, the spacing between the adjacent teeth, the biting surfaces of the opposing teeth, and the vertical and horizontal alignment of the teeth as part of the dental arch.
The dominant method currently used to achieve the required alignment is a dental impression, which provides a geometrically precise, 3-dimensional model of the area. While successful, this method requires multiple office visits in order to be used. These visits prolong the process, increase cost, and take up chair time that could be used for other patients. Some concepts have been developed, primarily for use on an individual tooth, wherein only a single office visit is necessary. For example, in Sirona's CEREC system (Sirona Dental Systems GMBH, Bensheim, Germany), an optical scanning procedure is used to replace the conventional impression. In this system, an optical impression is imaged using structured light, and computer-based methods are used to determine the size and shape of the desired prosthesis. Computer-based methods are also used to create the prosthesis.
There are other methods that do not make use of a dental impression. Instead of a physical impression, these methods use direct images or scans of the patient's teeth. For example, U.S. Pat. No. 5,604,817, entitled “Tooth Measurement without Calibration Bodies” and issued to Massen et al. on 18 Feb. 1997, describes a method for the optical three dimensional measurement of a tooth without the use of calibration bodies arranged around the tooth. An optical projection system projects a pattern onto a tooth, and an optical imaging system images the pattern projected thereon, from a first position in space and subsequently from a second position in space, with the images from the two positions in space having a common imaged area of the tooth. The image patterns are evaluated to calculate three dimensional coordinate data of the tooth surface relative to the respective imaging position for each image and also for the two images combined, to produce a single three dimensional tooth surface data record. U.S. Pat. No. 5,372,502, entitled “Optical Probe and Method for the Three-Dimensional Surveying of Teeth” and issued to Massen et al on 13 Dec. 1994, describes an optical oral or mouth probe which is utilized for the three-dimensional measurement or surveying of teeth. The probe projects a particular pattern onto the teeth, which is distorted by the teeth. The measuring probe captures the distorted pattern and transmits it to a computer, which recreates the topography of the teeth.
In commonly-assigned, copending U.S. patent application Ser. No. 09/894,627, entitled “Method and System for Creating Dental Models from Imagery” and filed in the names of J. T. Boland, J. P. Spoonhower and J. R. Squilla, a dental model is created from a series of images of an intra-oral object, where the object includes common surface features and a control target arranged with respect to the object to provide control features. The common features, and the control features from the control target imaged with the images of the object, are measured for a series of images. Then a 3-dimensional model of the object is analytically generated by photogrammetrically aligning the measurements of the control features. The model is then adjusted by aligning the common features of the model to like features on the image of the intra-oral object, thereby producing an aligned dental model from the series of images.
In U.S. Pat. No. 6,068,482, entitled “Method for Creation and Utilization of Individualized 3-Dimensional Teeth Models” and issued to Michael Desmond Snow on 30 May 2000, a standard 3D model of a standard patient's teeth is individualized for a specific patient. A combination of the standard 3D model and either a scanned 2D x-ray image or a scanned 2D image of a plaster cast impression taken of the patient's teeth is projected by a computer system, where the x-ray image or the plaster cast image is projected as a background for the standard 3D model. The standard 3D model is then rotated, translated and scaled by the user so as to match the orientation of the background image. The resultant optimized 3D individualized model is then saved and used as a patient record for treatment planning and record keeping. In one described usage in an orthodontics practice to demonstrate the effect of braces, the differences between the standard model and the individualized model are mapped, and the computer system “animates” the differences to illustrate the movement of the teeth during treatment from the individualized model to the idealized standard model.
In using the direct imaging method of the prior art on multiple teeth, especially if dental impressions are not used, then the precise curvature data (of the teeth as part of the dental arch) is needed from another source. The present invention makes use of dental radiographs to geometrically describe the vertical alignment of a patient's teeth, which provides the needed information. By projecting the x-ray, a fitted curve, or the outline of the teeth onto a computer representation of the prosthesis (prior to fabrication), the vertical alignment of the arch (as indicated by the size, position and orientation of the teeth) can be confirmed and/or adjusted.